A typical Charge Trans-Impedance Amplifier CTIA-based IR pixel using a single ended OPAMP is shown in FIG. 1. In this figure, VAVDD is the OPAMP power supply (i.e., VDD_AMP). FIG. 1 shows a single pixel 100, that has an IR photodetector 105. A single ended op amp 110 is shown that has four (4) different transistors. This is shown in this way, with other transistors, such as cascode transistors, being eliminated to further reduce the pixel area/size. A reset transistor 115 is shown as a switch across a feedback capacitor (C_FB) 120.
The circuit also includes a signal sampling capacitor (C_SIG) 125 that holds the value of the pixel ones sample. The output stage 130 produces the output.
Using a single ended OPAMP in this way in the CTIA IR readout circuit can minimize the number of transistors that exist in the pixel. This in turn allows reducing the pixel size to provide for smaller pixel, large format IR image sensor applications.
However, such a single ended OPAMP in CTIA circuit has a very poor power supply rejection ratio, for example on the order of 0 dB. This means that, noise from the power supply will be directly coupled to the CTIA output. The noise could be very high in a large format sensor.